Reaction vessel comprising electrically conducting polymer as a heating element

ABSTRACT

A reaction vessel for conducting a chemical or biochemical reaction, such as a polymerase chain reaction wherein electrically conducting polymer is arranged to act as a heating element. The profile of the electrically conductive polymer differs in different regions of the vessel so as to control thermal gradients. The profile of the electrically conductive polymer may be arranged to either increase or reduce the thermal gradient. Reaction systems comprising combinations of vessels of the invention and apparatus for heating them, as well as particular reactions vessels are also described and claimed.

The present invention relates to reaction vessels useful in chemical andbiochemical reactions which are required to undergo controlled heatingand/or cooling, in particular, vessels which are required to undergothermal cycling, where a sequence of different temperatures arerequired.

A particular example of such a reaction are a number of nucleic acidamplification methods, in particular the polymerase chain reaction(PCR). As is well known, in this reaction, exponential amplification ofnucleic acids is achieved by cycling the sample containing or suspectedof containing the target nucleic acid through an iterative sequence ofdifferent temperatures in the presence of specifically designed primersequences and polymerase enzymes able to extend those primer sequences.These temperatures represent the temperatures necessary for nucleic aciddenaturation (and generally requires temperatures of about 95° C.),primer annealing (at a lower temperature for example at about 55° C.)and primer extension (which may require and intermediate temperature forexample of about 74° C.).

There is frequently a need to obtain the results of a PCR reactionquickly, for example in cases of environmental contamination which maybe the result of hostile activity. However, even in a clinical ordiagnostic situation, the production of quick results can be helpful, inparticular where patient compliance or return can be problematic.

Clearly, for fast PCR, the sample must be rapidly heated and cooled.This is facilitated by making the sample small to reduce its thermalmass and by minimising the distances over which heat must betransferred. The same considerations must be applied to the container ofthe sample.

Thus, a number of examples of apparatus designed to carry out PCRreactions utilize reaction vessels which comprise a capillary tubeformat (ie long and thin WO 2005/019836) or as a planar structure (flatand thin) (WO2006024879), the content of which are incorporated hereinby reference.

A variety of heating systems are utilized in order to achieve rapid PCR.These include for example fluid based systems in which hot fluid such asair is fed to the container of the sample for heating purposes, andnon-heated fluid is supplied to effect cooling (see for example U.S.Pat. No. 6,787,338 and WO2007/054747, the content of which isincorporated herein by reference).

In an alternative type of apparatus, electrically conducting polymer(ECP) is used as both the heating element and in some cases also thecontainer (see WO 98/24548, the content of which is also incorporatedherein by reference).

The ECP acts as a resistive heater and so it is required to be connectedto an electrical supply by way of electrical connections. As aninevitable consequence of reducing the thermal mass of the sample andfacilitating heat transfer into and out of it, the means of connectingand locating the ECP can have significant thermal effects upon it.

A particular problem is the formation of temperature gradients as heatcan be conducted both out from and in to the extremities of the ECPtube, through the electrical connections, as it is heated and cooled,respectively.

This problem has been addressed in some instances by examining theelectrical connections themselves and in particular, the mountings forthe electrodes. These must be electrically insulating and are preferablyalso thermally insulating. However, the property of thermal insulationis in itself insufficient.

Electrical connectors (or electrodes) that are thermally insulating heatand cool slowly which has the effect of making them importantcontributors to the formation of longitudinal temperature gradientsduring rapid thermal cycling. The mountings must also therefore have alow thermal mass as well as being thermal insulators. This may beachieved by placing insulating materials that have been structured toreduce their thermal mass whilst retaining the physical integrity neededto support the electrodes. Such structuring, in its essence, requiresthe inclusion of air gaps in the mountings. This may be achieved byusing foam materials, such a honeycomb or reticulated foam to form amount for the electrode. The mounts are suitable in the form of apillared or corrugated mount for the electrical connector (as describedfor example in WO2005/0011834, WO2004/045772 and copending BritishPatent Application No. 0623910.7).

In PCR, it would be ideal to have all parts of the sample at the samecontrolled temperature all of the time. This is extremely difficult in asystem that is being rapidly heated and cooled. In the capillary format,both radial and longitudinal temperature gradients are formed.

The applicants have found however that the profile of the ECP can beadjusted to control the thermal gradient

A first aspect of the present invention provides a reaction vesselheating system, which comprises electrically conducting polymer,arranged to act as a heating element for a reaction vessel, wherein theprofile of the electrically conductive polymer differs in differentregions of the vessel so as to control thermal gradients therealong.

The ECP profile may be arranged to have the effect of reducing thermalgradients. This is particularly suitable for reaction vessels used forthermal cycling reactions, for example PCR.

In one embodiment, the profile of the ECP is itself adjusted to vary itsradial thickness so that the resistance heating is distributed unevenlyin a way so as to reduce gradients. This may be done empirically, inrelation to any particular vessel type, by determining the gradientprofile which occurs and adjusting the thickness of the ECP in variousregions of the vessel accordingly. Typically, the profile will betapered, being narrower at the bottom of the vessel than the top.Instead of varying the radial thickness, the area of contact between thevessel and ECP may be varied.

The thermal gradients may be further reduced by providing the vesselwith at least one wall which comprises a highly thermally conductinglayer. The highly thermally conducting layer may comprise a metalliclayer, for example aluminium. The electrically conductive polymer isinsulated from the metallic layer by means of an insulating layertherebetween, for example a layer of anodised aluminium, or is a polymerlayer, such as parylene or a derivative thereof. Preferably the vesselfurther comprises an inner non metallic layer to improvebiocompatability.

The reaction vessel may be an elongate vessel. In a preferredembodiment, the reaction vessel comprises a tube which is sealed at oneend, wherein the end is of a transparent material. The reaction vesselmay comprise a capillary vessel or a flattened capillary vessel.

In another embodiment, the ECP profile is arranged to have the effect ofincreasing thermal gradients. A thermal gradient is thus created alongthe vessel.

A vessel with a thermal gradient may be used for the culture ofbiological materials, with different regions along the thermal gradientbeing optimal for different biological material. The vessel may comprisea petri dish, cuvette, chemostat, shake flask, universal container,bijou.

The profile may be adapted by changing the radial thickness of ECP.Alternatively, the area of contact between the ECP and the vessel may bevaried.

A second aspect of the present invention provides a method for carryingout a chemical or biochemical reaction which requires at least oneheating step, said method comprising placing chemical or biochemicalreagents into a reaction vessel according to the present invention andheating said reagents so as to bring about a chemical or biochemicalreaction.

Preferably the reaction requires thermal cycling. More preferably thereaction is a polymerase chain reaction.

A third aspect of the present invention provides a method for mixingreagents in a vessel, said method comprising placing said chemical orbiochemical reagents in a reaction vessel according to the presentinvention and heating the heating the vessel so as to bring about atemperature gradient to thereby create convection.

Such modifications may be included in vessels which include or utiliseECP resistance heaters, irrespective of the presence or otherwise of thehighly thermally conducting layer, and such vessels form yet a furtheraspect of the invention.

According to a fourth of the present invention there is provided areaction vessel for conducting a chemical or biochemical reaction,wherein at least one wall of said vessel comprises a layer of a highlythermally conducting material, (in particular a metallic layer) and aninner non-metallic layer.

For the avoidance of doubt, the term “layer” as used herein refers toany essentially laminar arrangement of material, including bothself-supporting layers as well as coatings. Layers or coatings which arenot self supporting, will generally conform to the shape of the relevantsubstrate, and so for example may in practice may be any shape,including in particular tubular. Similarly, self-supporting layers maytake whatever form is particularly convenient in relation to the contextin which they are used.

Reaction vessels of the invention have good thermal conductivity as aresult of the presence of the highly thermally conducting layer of thewall, and therefore can be used in reactions where temperature control,or in particular temperature cycling with good temperature uniformity isimportant. Therefore, they may be particularly useful in reactions suchas nucleic acid amplification reactions which involve thermal cyclingsuch as the polymerase chain reaction (PCR). The good thermalconductivity means that significant temperature gradients through thevessel do not form, or are rapidly evened out if they do occur, so thatthe temperature profile along and across the sample is made flatter(more homogeneous).

Generally, metal walled vessels have not be used hitherto in reactionvessels because they are generally chemically reactive in particularwith biological molecules such as nucleic acids and proteins, and so themetal interferes with reagents in the vessel and so disrupts thereaction. However, the applicants have found that this problem can beovercome by the provision of an inner non-metallic layer, in contactwith the thermally conducting layer such as the metallic layer so as toeffectively form a composite.

The vessel is suitably an elongate vessel, with the layered wall formingat least one of the long walls so as to increase the surface area of themetal containing wall which is in the proximity of a reagent in thevessel. In particular, the vessel is a capillary vessel or a flattenedcapillary vessel, where the length is selected to accommodate the volumeof the sample and inner diameters are small. In particular, the innerdiameter of a capillary tube is in the range of from 0.2 to 2 mm. Thethickness of the wall is generally from about 0.1 to about 1.5 mm.

Examples of such vessels are described for example in WO2004/054715,U.S. Pat. No. 6,015,534 and WO 2005/019836, the content of which isincorporated herein by reference.

Such vessels effectively comprise a single radial side wall and thissuitably comprises a metallic layer over substantially all, andpreferably all its area.

Where flattened tubes are used, they may be of a shape described inWO2006024879, the content of which is incorporated herein by reference.Specifically, such vessels have a width:depth ratio of about 2:1 ormore, for example, of 3:1 or more. Typically the width of the vesselsmay be of the order of 1 mm or less for example 0.8 mm or less, whereasthe depth is generally 0.5 mm or less, and suitably less than 0.3 mm.The vessels may be tapered.

In these cases, at least one side wall comprises a metallic layer, andpreferably all side walls comprise a metallic layer. The lower wall mayalso have this construction, although in many instances, it is preferredthat the lower wall, which forms the base of the vessel is of atransparent material such as glass or a transparent polymer so that thecontents of the reaction vessel can be optically monitored during thereaction. This is particularly helpful in the case of the use of theso-called “real-time” PCR reactions where optical signals, in particularfluorescent signals from signalling reagents added to the PCR reaction,produce a variable signal as the reaction progresses, so that theprogress of the reaction can be monitored. Such monitoring gives rise tothe option of quantifying the amount of target nucleic acid within theinitial sample, so providing further information which may be of use,for example in diagnostics, in determining the seriousness of aparticular condition.

Suitable non-metallic materials for the inner non-metallic layers mayinclude polymeric materials or glass or even a passivated layer createdthrough anodisation of a metal, or similar process, or combinations ofthese. In particular, however, the inner non-metallic layer is a polymeror glass or combination of these.

In a particular embodiment, the inner non-metallic layer is a glasslayer, since glass is generally well recognised as being compatible withmany biochemical and chemical reactions including the polymerase chainreaction.

However, polymeric materials such as polyurethane, polyethylene,polypropylene, or polycarbonates, as well as silicones which arecompatible with the sample and with the particular reaction beingcarried out within the reaction vessel.

Such inner layers will generally be rigid and supporting structures,which may be formed by processes such as injection or extrusion mouldingand the like. These may then be coated with a metallic layer, or theymay be extruded or formed directly onto the metallic layer.

However, if necessary or required a thin layer for example of polymericmaterial may deposited on the metallic layer for example usingtechniques such as vapour deposition, liquid phase deposition or plasmapolymerisation to provide a relatively thin layer which may itselfconstitute the inner non-metallic layer. Alternatively, such a thinlayer may be applied to a different inner non-metallic layer asdescribed above to form a composite structure.

A particularly suitable polymeric layer of this type is formed ofparylene or derivatives thereof. Parylene is a generic name applied topolyxylylene as for example as described in U.S. Pat. No. 3,343,754, thecontent of which is incorporated herein by reference.

Compounds of this type can be represented by the general formula (I)

where is R is a substituent group, m is 0 or an integer of from 1 to 3and n is sufficient for the compound to be a polymer.

Where m is greater than 1, each R group may be the same or different.

In one embodiment, m is 0.

Suitable substituent groups R include but are not limited to R¹, OR¹,SR¹, OC(O)R¹, C(O)OR¹, hydroxyl, halogen, nitro, nitrile, amine, carboxyor mercapto and where R¹ is any hydrocarbon group and where R¹ may beoptionally substituted by one or more groups selected from hydroxyl,halogen, nitro, nitrile, amine or mercapto.

Suitable hydrocarbon groups include alkyl groups such as straight orbranched chain C₁₋₁₀alkyl groups, alkenyl groups such as straight orbranched C₂₋₁₀alkenyl groups, alkynyl groups such as straight orbranched C₂₋₁₀alkynyl groups, aryl groups such as phenyl or napthyl,aralkyl groups such as aryl (C₁₋₁₀) alkyl for instance benzyl,C₃₋₁₀cycloalkyl, C₃₋₁₀cycloalkyl (C₁₋₁₀) alkyl, wherein any aryl orcycloalkyl groups may be optionally substituted with other hydrocarbongroups and in particular alkyl, alkenyl or alkynyl groups as describedabove.

Particular examples of groups R include alkyls such as methyl, ethyl,propyl, butyl or hexyl, which may be optionally substituted withhydroxy, halo or nitrile such as hydroxymethyl or hydroxyethyl, alkenylssuch as vinyl, aryls in particular phenyl or napthyl which may beoptionally substituted by halo or alkyl groups such as halophenyl orC₁₋₄alkylphenyl, alkoxy groups such as methoxy, ethoxy, propoxy,carboxy, carbomethoxy, carboethoxy, acetyl, propionyl or butyryl.

In particular, R is selected from halogen (particularly chlorine orbromine), methyl, trifluoromethyl ethyl, propyl, butyl, hexyl, phenyl,C₁₋₄alkylphenyl, naphthyl, cyclohexyl and benzyl.

Examples of such polymers are sold as “Parylene”. Particular variety ofparylene which may be obtained include Parylene N (where m is 0),Parylene C (where m is 1 and R is chloro), Parylene F (where m is 1 andR is trifluoromethyl) and Parylene D (where m is 2 and each R ischloro).

Parylene is a particularly convenient polymeric material for providingan internal coating for the metallic surface, as it may be readilyapplied using a vapour deposition process. In this process a solid dimerof formula (II)

where R and m are as defined above, is placed into a suitablevaporisation chamber in solid form. When the chamber and heated underreduced pressure, for example to temperatures of about 150° C. at lowpressure, for example of about 1 mmHg, the diner vapourises. The vapouris then transferred into a pyrolysis chamber where the temperature ismuch higher, for example at about 650° C. and the pressure is forexample of 0.5 mmHg, Pyrolysis occurs so as to cause the formation of areactive monomeric species of formula (III).

If this is allowed to pass into a further chamber containing the item tobe coated which is at ambient temperature, but also at low pressure, forexample of 0.1 mmHg, polymerisation of the species (III) occurs on thesurface of the object, so that a coating of the polymer of formula (I)above is produced.

The species (III) condenses on the surface in a polycrystalline fashion,providing a coating that is conformal and pinhole free. This isimportant to ensure that any sample within the reaction vessel isisolated from the metallic layer.

Compared to liquid processes, the effects of gravity and surface tensionare negligible—so there is no bridging, thin-out, pinholes, puddling,run-off or sagging. And, since the process takes place at roomtemperature, there is no thermal or mechanical stress on the object.

Parylene is physically stable and chemically inert within its usabletemperature range, which includes the temperatures at which PCRreactions are conducted. Parylene also provides excellent protectionfrom moisture, corrosive vapours, solvents, airborne contaminants andother hostile environments.

It is widely used in the electronics industry to coat and protectelectronic components. However, the applicants are the first to findthat parylene is compatible with chemical or biochemical reactions andin particular with the PCR reaction, and the use of parylene for coatingreaction vessels and in particular PCR reaction vessels is described andclaimed in the applicants copending patent application of even date.

In the vessel of the apparatus, the metallic layer effectively forms athermal shunt, conducting heat rapidly from one part of the reactionvessel to another. Thus it minimises the build-up of thermal gradientsin the vessel and therefore in the sample during the reaction, which isimportant in ensuring that the reaction proceeds efficiently and well.

Thus vessels comprising a highly thermally conducting material mostsuitably comprise a material which has a thermal conductivity in excess15 W/mK. Materials having this property will generally be metallic innature, but certain polymers, in particular those known as “coolpolymers” or polymers containing thermally conducting ceramics such asboron nitride as well as diamond, may have the desired level of thermalconductivity. In particular however, the highly thermally conductingmaterial is metallic, which may be of any suitable metal or metal alloyincluding aluminium, iron, steel such as stainless steel, copper, lead,tin or silver. In particular, the metallic layer comprises aluminium.

The reaction vessel in accordance with the invention, may be heated byany suitable heating means, and as a result of the presence good thermalconductivity of the walls of the vessel due to the presence of thehighly thermally conducting layer, the heat will be readily transferredto the vessel contents.

Thus the vessels are suitable for use in a wide range of apparatus inparticular thermal cycling equipment. These may be heatable and/orcoolable using a number of different technologies, including the use offluid heaters and coolers such as air heaters and coolers in particularthose heated by halogen bulbs, as described for example in U.S. Pat. No.6,787,338 and WO2007/054747, the content of which is incorporated byreference, as well as in vessels using ECP as resistive heatingelements, for example as described in WO 98/24548 and WO 2005/019836 aswill be discussed further below. The vessels may also be used in moreconventional devices such as solid block heaters that are heated byelectrical elements. For cooling the apparatus may incorporatethermoelectric devices, compressor refrigerator technologies, forced airor cooling fluids as necessary. However, where the vessels of theinvention comprise a metallic layer, this means that they may also becapable of being heated using for example induction methods. Apparatusused to heat vessels of the invention in this way will have the facilityto heat the vessel by electromagnetic induction, for example by using ahigh-frequency alternating current (AC) to induce eddy currents withinthe metal. Resistance of the metal to these currents leads to Jouleheating of the metal. Heat is also generated by magnetic hysteresislosses. For use in induction heating apparatus, it will be clear thatthe metallic layer within the vessel should be of a suitable material toallow it to be heated in this way, and so for example iron metalliclayers may be preferred to say stainless steel or copper.

Reaction systems comprising combinations of reaction vessels asdescribed above, and apparatus which is able to accommodate saidreaction vessel, and which comprises a heating system adapted tocontrollably heat and cool said vessel, in particular using any of themethods discussed above, form a further aspect of the invention.

When the reaction vessels of the invention are utilised in combinationwith resistive heating elements, such as ECP, it is necessary to ensurethat where the highly thermally conducting layer is also electricallyconducting, such as a metallic layer, this is electrically insulatedfrom the resistive heater in order to prevent short circuits etc. Theapplicants have found that it is possible to passivate the surface of ametal layer so that it is electrically isolated from the ECP, but stillin good thermal contact. For example in the case of an aluminiummetallic layer, anodisation of any surface of the aluminium layer whichis to be in contact with the resistive heater such as the ECP providessuch insulation.

Alternatively, a parylene layer, preparable as described above may beapplied to the surface of the highly thermally conducting layer such asthe metallic layer which contacts the ECP so as to provide an effectiveelectrically insulating layer. Such layers have the benefit that they donot significantly add to the size or thermal mass of the vessel.

The ECP is suitably arranged as a sheath or coating arranged outside thehighly thermally conducting layer and the electrically insulating layerthereof, as described in WO 98/24548. By keeping the elements of thereaction vessel small, in particular as thin layers, the thermal mass ofthe vessel remains low, and so fast heating and cooling can take placeas is required for rapid PCR.

Thus in a particularly preferred embodiment, a wall of the reactionvessel, and suitably the entire side walls of the vessel comprise aninner non-metallic layer, for example of glass or a polymeric material.This is covered by a metallic layer as described above, which is itselfcovered by an electrically insulating layer, for example a layer ofanodised aluminium or parylene or a derivative thereof as describedabove. Outside of this layer is suitably provided a layer ofelectrically conducting polymer. Such vessels are generally intended tobe disposable after a single use.

The electrically conducting polymer needs to be connected to anelectrical supply, and so electrical connections, which may be integralwith the vessel, are suitably provided at each end of the ECP.

The ECP elements used in the vessels as resistive heating elements canbe manufactured by various processes, but most a convenient processinvolves injection moulding of the polymer. However, in the process ofinjection moulding, the material tends to form an outer polymer-richskin that may creates at least a partial electrically insulating barrierto any external means of making electrical contact.

In such cases, the applicants have found that it is helpful to breakthrough the insulating skin and make electrical contact with the bulkmaterial in order to increase the efficiency of the heating system.

Thus, in a particular embodiment, the reaction vessel as describedabove, is connectable to an electricity supply by means of barbedelectrical contacts which pierce the surface of the electricallyconducting polymer. These are suitably integral with the vessel.

Such barbed connectors may take various forms depending upon theparticular configuration of the reaction vessel itself. In particular,where the vessel is of a generally tubular configuration, suitablebarbed connectors may take the form of annular metal rings with inwardlyprojecting barbs or the like, similar in design to “Starlock Washers”.

The inwardly projecting barbs will cut through the insulating skin tomake electrical contact with the bulk conducting material, as well ashold the ring in position. The outer portion will present a metallicsurface for electrical interconnection, and so apparatus intended toaccommodate the vessels will be configured appropriately.

Furthermore, the barbs provide effectively a scalloped edge which helpsto reduce the size and therefore the thermal mass of the connectors andalso, reduces the contact area with the ECP. This has the furtheradvantage of further minimising heat exchange between the electricalconnectors and the ECP, so further assisting in reducing unwantedthermal gradient formation.

The connectors and particularly the barbs thereof, are suitablyconstructed of a material which have high mechanical strength, so thatthe barbs can be sharpened to enhance the penetration ability. Whilstmany metals are able to fulfil this function, a particularly suitablematerial for the connectors has been found to be stainless steel. Thisnot only has the required mechanical strength and electricalconductivity, but also, it has a high corrosion resistance, at 16 W/mK,a surprisingly low thermal conductivity compared to many other metals(cf Copper @ 399 W/mK, Aluminium @ 237 W/mK). By using this material,and by designing the connectors so that their area is as small aspossible, helps to reduce unwanted thermal effects at the electrodes.

Connections of this type are cost effective to manufacture, which willbe a particular advantage in cases where the proposed PCR vessel is tobe a high volume disposable item.

They may, in fact, be used in connection with any reaction vessel ordevice which includes ECP as a resistive heater, and such reactionvessels and devices form a further aspect of the invention.

As discussed briefly above, the apparatus into which the vessel isaccommodated for use suitably is provided with mounts of a materialwhich is both an electrical and thermal insulator (i.e the materialabsorbs and releases heat slowly) and also have a low thermal mass. Thiscan be achieved by making the electrode mounts “air-like” ie formed asfoam, skeletal or honeycomb structures. However they must be able tophysically support and position the electrodes, and therefore they musthave a degree of rigidity, firmness and/or resilience.

Thus in a particular embodiment of the apparatus for thermally cyclingthe contents of the reaction vessel as described above comprises a solidfoam material arranged in direct contact with at least one of saidelectrical contacts.

The solid foam material acts as an insulator, preventing heat flows andparticularly heat loss through the electrical contacts. As a result, amore uniform temperature can be maintained within the reaction vessel.By utilising specifically a solid foam in preference to a conventionalsolid insulator, such as a solid plastics insulator, the performance ofthe apparatus is significantly enhanced. Thermal gradients set up withinthe reaction vessel can be further reduced.

It is believed that this is due to the fact that foam-like materialshave a lower thermal mass than solids. Therefore, in addition toproviding insulation preventing the flow of heat into and out of thereaction vessel through the electrical contact, they do notsignificantly hinder the heating and cooling process.

In contrast, solid insulators with significant thermal mass were foundto heat up and cool down slowly (rather than not at all), thereby actingas sources or sinks of heat depending on their temperature relative tothe sample. This was found to be disadvantageous in this context.

Suitable solid foam materials include metal, glass, carbon, polymer,ceramic foams or composites made of several of these.

Particular examples of such foam materials are polymeric foams such aspolyurethane or polystyrene foams.

In a particular embodiment, the foam material is a ceramic foam. Ceramicfoams generally comprise inorganic, non-metallic materials (such asmetal oxides, silicides, nitrides, carbide or borides) with acrystalline structure, which have usually been processed at a hightemperature at some time during their manufacture.

Many such foams are now commercially available. They have been developedmainly for the aerospace industry where their utility as insulators is aresult of their light weight.

Solid foams generally comprise solids which have many gas bubblestrapped within them. They may be rigid or pliable in nature, but arepreferably rigid so as to support the electrical contacts. Where theyare pliable, the foam material suitably has a good “shape memory”.

Various forms and types of solid foam materials are known. Some areknown as “refractory” foams. They are made by various methods dependingupon the nature of the material used. For instance, solid foamscomprising polymers may be readily prepared including foaming agentsinto the preparation process, as is well understood in the art.Syntactic foams and self-foamed materials such as foam glass may beprepared in a similar way.

Other solid foams may utilise a foamed polymer as the basic startingmaterial and materials are essentially coated onto these or ontocarbonaceous skeletons formed by pyrolysis of the polymer foam. Forexample, ceramic foams can be produced by coating a polymer foam or acarbon skeleton derived from it, with an appropriate binder and ceramicphases, and then sintering at elevated temperatures. Metallic foams maybe formed by electrolytically depositing the metal onto a polymer foam,utilizes an electrodeless process for the deposition of a metal onto thepolymer foam precursor via electrolytic deposition.

Suitably the solid foam material is of a material, which has nofluorescent or phosphorescent properties, even when illuminated with alight source. This means that it may not interfere with the fluorescentsignalling or labelling systems that are frequently utilised fordetecting the products of an amplification reaction. Such systems may beused to detect the product of amplification either at the end point ofthe reaction, or, increasingly, in “real-time” as the reactionprogresses. These systems, which include the well known “Taqman™” systemas well as other systems such as those described for example inHomogeneous fluorescent chemistries for real-time PCR. Lee, M. A.,Squirrell, D. J., Leslie, D. L. and Brown, T. in Real-time PCR: anessential guide, J. Logan, K. Edwards & N. Saunders eds., HorizonScientific Press, Wymondham, p. 31-70, 2004, the content of which isincorporated herein by reference. For instance, generic methods utiliseDNA intercalating dyes that exhibit increased fluorescence when bound todouble stranded DNA species. Fluorescence increase due to a rise in thebulk concentration of DNA during amplifications can be used to measurereaction progress and to determine the target molecule copy number.Furthermore, by monitoring fluorescence with a controlled change oftemperature, DNA melting curves can be generated, for example, at theend of PCR thermal cycling.

However, when the material has a degree of fluorescence, this may beobviated by dying, coating or inking the foam before use.

The solid foam material is arranged in contact with at least one andpreferably both of the electrical contacts. Suitably sufficient foammaterial is arranged so that in use, it effectively isolates theelectrical contacts from environmental effects. This will generally beachieved by arranging the solid foam material in contact with at leastthe remote edges of the electrical contacts.

If desired, a solid insulator material may also be provided and arrangedto contact the solid foam material.

Suitable solid insulator materials are well known in the art, andinclude polymeric or fibrous materials. In particular the solidinsulator is a polymeric insulator such as an acetal homopolymer resinsuch as Delrin™, acrylonitrile-butadiene-styrene terpolymer (ABS) orpolytertrafluoroethylene (PTFE).

The solid insulator may be arranged to contact a substantial portion,for example at least one side of the solid foam material. Thisadditional insulation will protect the solid foam material itself fromchanges in environmental temperature and so enhance the overallreliability of the system. Suitably the additional solid insulator isprovided so as to effectively isolate the reaction vessel from theexternal environment when in use. The precise arrangement of the solidinsulator therefore will vary depending upon the nature of the reactionvessel and the manner in which it is used.

As mentioned above, example of mounts which include foam-like materialsare described for example in WO2005/0011834, WO2004/045772, where thefoam materials have a degree of resilience or compliance to allow themto hold the connectors firmly, or co-pending British Patent ApplicationNo. 0623910.7, where firm foam-like materials may be used, which aresprung-loaded to ensure that a sufficiently firm hold on the connectorsis achieved.

Reaction vessels as described above and reaction systems comprising themcan be used in chemical and biochemical reactions as required. Thus, ina further aspect, the invention provides a method for carrying out achemical or biochemical reaction which requires at least one heatingstep, said method comprising placing chemical or biochemical reagentsinto a reaction vessel as described above, and heating said reagents soas to bring about said chemical or biochemical reaction. In particular,the vessel is positioned into apparatus specifically designed to holdit, and to heat and/or cool it as required. In particular, the apparatuscomprises a thermal cycler as described above, and the reaction requiresthermal cycling, in particular is a polymerase chain reaction.

The invention will now be particularly described by way of example withreference to the accompanying diagrammatic drawings in which:

FIG. 1 shows a section through a reaction vessel according to theinvention;

FIG. 2 shows an enlarged view of the portion of the reaction vesselshown in claim 1, which incorporates the elements of the invention;

FIG. 3 is a perspective end view of the reaction vessel of FIG. 1; and

FIG. 4 shows an electrical connection used in the embodiment of FIG. 3;and

FIG. 5 is a schematic diagram showing a vessel as shown in FIG. 1 inposition in a thermal cycling apparatus.

FIG. 6 illustrates a sample vessel coated with ECP, showing tapering ofthe ECP layer;

FIG. 7 is a graph illustrating the internal temperatures of a samplevessel at a thermopile setting of 43° C.;

FIG. 8 is a graph illustrating the internal temperatures of a samplevessel at a thermopile setting of 63° C.;

FIG. 9 is a graph showing the effect of tapering the ECP at differentthermopile settings; and

FIG. 10 is a graph showing the different temperatures recorded on atapered section of ECP.

The reaction vessel shown in FIG. 1 is of the same general type as thosedescribed in for example WO2005/019836, which is intended for use in anapparatus for conducting a PCR reaction.

The vessel comprises a plastics body (1) with an upper sample receivingportion (2) with a relatively wide mouth so that reagents can, withease, be added. In the illustrated embodiment, the upper portionincludes projecting flanges (6) which are able to interact with alifting arm in an apparatus such as that described in WO 2005/019836 soas to allow the vessel to be moved in an apparatus adapted to carry outreactions automatically.

At the lower end of the sample receiving portion (2), the vesselterminates in a capillary tube (3) which is sealed at the lower end by atransparent seal (4), so as to form an elongate thin reaction vessel,which can contain relatively small sample (7) within the capillarysection.

An aluminium coating layer (5) surrounds the capillary tube (3) and isin close thermal contact with it. This coating layer (5) acts as athermal shunt, which is able to rapidly dissipate thermal gradientswhich build up along the tube (3) and thus within a sample (7) which issubject to heating and/or cooling. The outer surface of the aluminiumcoating layer (5) has been anodised so as to produce an insulating layerthereof. In an alternative embodiment however, the outer surface of thealuminium coating layer (5) is coated with parylene to provideelectrical insulation.

An ECP layer (8) completely encases the aluminium coating layer (5) aswell as the sides of the lower seal (4) and the base of the upperportion (2). Is it provided with upper and lower ridges (9, 10)respectively which can accommodate upper and lower annular electricalconnectors (11, 12) respectively. Each electrical connector (11,12) isprovided with a number of inwardly projecting barbs (13) (FIGS. 3 and 4)which are able to pierce the surface of the ECP to ensure thatelectrical contact is made with the body of the ECP.

In use, this particular vessel can be loaded with sample and PCRreagents, as described in WO 2005/019836. A prepared sample (7) to whichhas been added all the reagents necessary for carrying a PCR reaction isplaced in the upper portion (2) and if necessary a cap (not shown) isplaced over open end. The entire vessel is then then centrifuged toforce the sample (7) into the capillary tube (3) section of the vessel.

In an alternative embodiment however, the sample and the reagents may beloaded directly into the capillary tube (3) using a specificallydesigned fine tipped pipettor, and with accompanying close control ofpipettor removal, as described and claimed in a copending British patentapplication of the applicants of even date to the present application.

The vessel is then suitably positioned in an apparatus (FIG. 5) able toaccommodate it such that the connectors (11, 12) are connectable to anelectrical supply but seat on a pair of supports.

A ring of a solid foam insulator material (14) (a polyurethaneengineering foam) is provided in contact with the lower edge portion ofthe upper electrical contact (11). The lower electrical contact (12) isheld on a shaped support (15), also of the solid foam insulatormaterial.

The solid foam insulator material is arranged to minimise heat transferfrom the electrical contacts, but does not interfere with the contact tothe electrical supply (not shown).

A ring (16) of solid insulator material such as Delrin is providedadjacent the ring of solid foam insulator material (14) in contact withit. The ring (16) effectively surrounds the rest of the upper electricalcontact (11) but is not in direct contact with it. As a result, it actsas an insulator from environmental effects coming from above, but doesnot act as either a heat sink or heat source in relation to theelectrical contact itself.

Similarly, the shaped support (15) of a solid foam insulator material isitself supported on a ring (17) of solid insulator material such asDelrin so as to provide similar protection for the lower electricalcontact (5). The solid insulator rings (16, 17) are provided withconduits for electrical connection and spring-mounted in housing (18).

In use, the solid insulator rings (16, 17) combined with the apparatusin which the vessel is held define a chamber for the tube (2) that iseffectively isolated from the environment. However, the electricalcontacts themselves are in contact with the solid foam material of lowthermal mass.

When arranged in this way, the apparatus could be utilised in apolymerase chain reaction in a far more effective and reliable manner,as compared to devices which had no or alternative arrangements ofinsulator material.

The connectors (11,12) are then connected to the electrical supply,which is controlled, suitably automatically, to pass current through theECP layer (5) so it rapidly progresses through a series of heating andcooling cycles, ensuring that the sample is subjected to similar cyclingconditions. This will allow the sample (7) to be subjected to a PCRreaction.

Where a real-time monitoring system is included in the sample (7), theprogress of the PCR can be monitored through the seal (4) usingconventional methods.

As a result, rapid PCR can be achieved. The presence of thermalgradients within the vessel (1) and therefore the sample (7) is reducedby the measures taken, including in particular the presence of thealuminium coating layer (5) which acts as a thermal shunt. Thus reliableand reproducible results may be achieved.

During thermal cycling of the sample vessel in the PCR process,temperature gradients can arise along the length of the vessel. Thesetemperature gradients typically arise due to the influence of theelectrical connections, the temperature being higher in the regionadjacent to the electrical connections during heating due to conduction.The applicants have discovered that the thermal gradients can beminimised by tapering the ECP coating of the sample vessel.

FIG. 6 illustrates the sample vessel of FIGS. 1 and 2. As previouslydescribed the sample vessel has a lower portion comprising a capillarywhich is coated in ECP. The capillary is 11.6 mm and FIG. 6 shows theradial thickness of the ECP at three positions along its length. The ECPtapers from an area of 3.12 mm at the top, 2.78 mm in the middle and2.51 mm at the bottom.

FIGS. 7 and 8 show experimental data measuring the internal temperatureof three sample vessels, having different radial thicknesses of ECP atthe tip. The three sample vessels had uniform thickness of ECP along thelength, apart from the tip 27, which had different adjustment to the tipdiameter.

FIG. 7 illustrates the mean, tip and centre internal capillarytemperatures at a thermopile setting of 43° C.

FIG. 8 illustrates the mean, tip and centre internal capillarytemperatures at a thermopile setting of 63° C.

Both sets of results show that when the tip diameter was reduced,causing a tapering of the ECP, the different between the temperature atthe tip and centre was also reduced.

FIG. 9 shows the effect of tapering the ECP on the temperature gradientinside the capillary, showing results for thermopile settings at both43° C. and 63° C. It can be seen that reducing the tip diametersignificantly reduces the temperature difference between the tip and thecentre and that the effect is increased for higher temperatures.

This effect of minimising temperature gradients by altering the ECPprofile can be further enhanced by the use of a layer of highlythermally conducting material, for example aluminium as described in theprevious embodiments.

The applicants have discovered that the profile of ECP can be adjustedto increase the thermal gradient. FIG. 9 shows that the temperaturegradient inside the capillary is increased when the tip diameter isincreased.

A temperature gradient caused by profiling ECP can be created asdescribed in the following example.

EXAMPLE

A 1 mm thick sheet of ECP (carbon black filled polyethylene) was cutinto the shape of an elongated equilateral triangle with the tip cutoff, having dimension of 90 mm long, 20 mm wide at the base and 4 mmwide at the tip. This was connected to a laboratory power supply usingcrocodile clips that were attached at either end.

A ruler was used to measure 10 mm steps (from the narrow end to the wideend) starting at 10 mm from the narrow end and finishing at 70 mm fromthe narrow end. The ECP was placed on a foam block and temperature ateach step was measured by placing a thermocouple probe on the surfacewith a small pad of foam on the top.

The temperature measurements are shown in FIG. 10. As can be seen, atemperature gradient is formed between the higher temperature at thenarrow end and the lower temperature at the wider end.

1. A reaction vessel heating system, which comprises electricallyconducting polymer, arranged to act as a heating element for a reactionvessel, wherein the profile of the electrically conductive polymerdiffers in different regions of the vessel so as to control thermalgradients therealong.
 2. A reaction vessel heating system according toclaim 1 wherein the profile of the ECP is arranged to have the effect ofreducing thermal gradients therealong.
 3. A reaction vessel heatingsystem according to any of claims 1 and 2 wherein at least one wall ofsaid vessel comprises a highly thermally conducting layer.
 4. A reactionvessel according to claim 3 wherein the highly thermally conductinglayer is a metallic layer.
 5. A reaction vessel according to any ofclaims 3 or 4 further comprising an inner non metallic layer.
 6. Areaction vessel according to any of claims 4 or 5 wherein theelectrically conductive polymer is insulated from the metallic layer bymeans of an insulating layer therebetween.
 7. A reaction vesselaccording to claim 6 wherein the insulating layer is a layer of anodisedaluminium, or is a polymer layer.
 8. A reaction vessel according toclaim 7 wherein the polymer layer comprises parylene or a derivativethereof.
 9. A reaction vessel according to any preceding claim which isan elongate vessel.
 10. A reaction vessel according to claim 9 whichcomprises a tube which is sealed at one end, wherein the end is of atransparent material
 11. A reaction vessel according to any one ofclaims 9-10 which comprises a capillary vessel or a flattened capillaryvessel.
 12. A reaction vessel according to any of claims 9-11 whereinthe radial depth of ECP material at the tip of the vessel is less thanthe radial depth of ECP material at the centre of the vessel.
 13. Areaction vessel according to any of claims 1-12 wherein the vessel is athermal cycling vessel.
 14. A reaction vessel according to any of claims1-113 wherein the vessel is a PCR reaction vessel.
 15. A reaction vesselheating system according to claim 1 wherein the ECP profile is arrangedto have the effect of increasing thermal gradients.
 16. A reactionvessel according to claim 15 wherein the vessel is a culture vessel forthe culture of biological materials.
 17. A reaction vessel according toclaim 16 wherein the vessel is one of a petri dish, cuvette, chemostat,shake flask, universal container, bijou.
 18. A method for carrying out achemical or biochemical reaction which requires at least one heatingstep, said method comprising placing chemical or biochemical reagentsinto a reaction vessel according to any one of claims 1 to 17 andheating said reagents so as to bring about a chemical or biochemicalreaction.
 19. A method according to claim 18 wherein the reactionrequires thermal cycling.
 20. A method according to claim 19 wherein thereaction is a polymerase chain reaction.
 21. A method for mixingreagents in a vessel, said method comprising placing said chemical orbiochemical reagents in a reaction vessel according to any of claims15-17 and heating the heating the vessel so as to bring about atemperature gradient to create convection.